#include <stdio.h>
#include <string.h>

int atoi(const char *s)
{
    int result = 0;
    int sign = 1;
    if (*s == '-')
    {
        sign = -1;
    }
    while (*s != '\0')
    {
        if (*s >= '0' && *s <= '9')
        {
            result = result * 10 + *s - '0';
        }
        s++;
    }
    return result*sign;
}
int main()
{
    const char *str = "-12345";
    int a = atoi(str);
    printf("%d\n", a);
    return 0;
}
